It is known in the prior art to control the operation of a workpiece shear in association with a hot strip rolling mill in accordance with the measured speed of the last roll stand as an indication of product travel distance and in accordance with the sensed head end of the work product by a hot metal detector. A speed reference signal is provided to the shear motor for controlling the rotation speed of the shear knife blade. It is known to provide a vernier adjustment to the determination of a present cut, when a similar previous cut was one of too early or too late, for moving in time the start of the speed reference ramp signal. If adequate motor current was not available for a previous similar length and speed cut of the work product, the home position of the knife blade was adjusted to result in a shorter travel distance with a more rapid acceleration. However, since the speed of the associated rolling mill can change between successive work products, the repositioning of the home or rest location of the knife blade is not a satisfactory solution to the problem of providing an adequate acceleration current energization of the shear drive motor to effect the desired cut of the work product. During a slow speed cut, a different home or rest position has been provided as required to result in a shorter travel distance and more motor current available to make the work product cut.
The conventional way of controlling a flying shear is to use a linear ramp speed reference signal from motor standstill to product cut. Since the acceleration rate is a function of the product velocity squared, this provides for a low speed product cut a motor acceleration rate which is too low for desired product cut operation of the shear.
It is known in the prior art as disclosed by U.S. Pat. No. 3,189,812 of M. A. Davis et al and U.S. Pat. No. 3,082,368 of W. D. Rowe to measure the velocity of a workpiece moving in relation to a shear and determine the necessary time delay before the shear is operated to cut a preset length from the head end of a workpiece and if desired to cut a preset length from the tail end of the workpiece. A reversible first counter is started to count in a first direction in response to signal pulses at a known frequency when the workpiece is detected by a first detector. When the workpiece reaches a second detector spaced a known distance from the first detector, the stored count of the reversible counter is transferred to a multiplier counter and the reversible counter begins to count in the opposite direction at a fractional frequency determined by the distance between the two detectors in relation to the distance between the second detector and the shear. At a predetermined count level of the first counter, the second multiplier counter responds to the signal pulses for controlling the shear.